Somewhere in the Chicago area, there is a prominent trial lawyer who gets his exercise by pedaling a stationary bicycle while listening to his cassette tape recorder.
He is not pedaling to the beat of the Rolling Stones or Lawrence Welk; he's listening to the latest tape from Chicago's Harris Bank. Once a month, a Harris spokesman says, this lawyer and about 1,200 other people receive the latest thoughts on investments and the economy on a cassette put out by the bank. Called ''Sound of Business,'' the half-hour tape includes a rotating cast of economists and investment specialists from the bank who, with the help of a moderator, hold a taped conversation about the latest economic trends and give their thoughts and projections for the future.
Harris Bank is one of several banks and investment advisory firms putting out cassettes on business and investments. Some of the cassettes have been going for several years - 13 years in Harris's case - but with the bullish stock market playing Pied Piper for thousands of first-time investors, there has been a noticeable increase of interest in actually hearing what the ''experts'' have to say.
Most of the listening is done at home or while commuting to work in the car. But that person you see jogging with a Walkman or barbecuing by the pool may just be listening to Citibank economists Leif Olsen or Alan Murray.
On Citibank's monthly tape, ''Sound of the Economy,'' several of the bank's economists talk about current economic trends, but not specific investments. On another cassette, ''Investor's Hotline,'' there are several dozen guest economists and forecasters, four of whom are used every month. And ''Newstrack'' selects articles from magazines and newspapers and has professionals read them. The tape includes general-interest stories as well as articles covering business and economic topics.
Until this year, the Harris spokesman recalled, cassette subscribers were happy just to hear macroeconomic views on interest rates, inflation, and world energy prices from the panel, which was made up entirely of economists. But after several requests for more specific investment information, including favored industries and companies, an investment specialist from the bank's trust department was made part of the quartet.
Investments are the main fare on ''Investor's Hotline,'' produced by Bradley Enterprises Inc. of Timonium, Md. The monthly tape, started in 1975, brings together stock market experts like Martin Zweig and Stanley Weinstein, economists such as Arthur Laffer and Frederick von Hayek, financial planners like Venita VanCaspel, and others - including some who have newsletters of their own - such as Howard Ruff, Albert Sindlinger, and Douglas Casey.
''Investor's Hotline,'' says Joseph Bradley, founder and president of the company, grew partly out of his existing business of taping corporate and investment seminars and distributing copies of the tapes, and partly out of his own growing interest in investments. ''I'd talk to some of these people (economists) and sometimes what they said would go right past me,'' he recalled, adding that he often taped the conversations. ''Then I'd listen to the tapes in the car or someplace. After that, I found my investment decisions were a lot better.''
Since the stock market started upward last August, interest in his cassette has increased, Mr. Bradley says, which is probably just the opposite of the way it should be.
''The best time to buy is often when the market is down,'' he notes. ''But generally speaking, that's not when people are as interested in information. People should be getting information when they're not really interested in it.''
Prices for these cassettes range from $100 for Harris Bank's monthly tapes to these prices are also receiving one or more printed investment newsletters in addition to the tapes.
Interestingly, says Richard Davis, editor of Citibank's ''Sound of the Economy,'' about half of his subscribers are listening to their tapes in another country. Mr. Davis admits he is puzzled by this overseas interest, but he has heard one explanation that he knows does not please everyone at the bank: language lessons.
''A lot of people in foreign countries don't get much chance to hear real conversational English,'' he says. ''This is sort of like a Berlitz course for them.'' And since each tape comes with a complete printed transcript, people who are just learning the language can also read the unfamiliar words they are hearing.
Mr. Davis wouldn't reveal exactly how many subscribers ''Sound of the Economy'' has, beyond saying they were in the ''tens of thousands.'' That would put the Citibank offering ahead of its competitors, assuming the figure is more than ''Newstrack's'' 14,000. The others have only a few thousand. But in the printed newsletter business, where costs are low and subscription rates are high , even 1,000 subscribers is often quite respectable.
Most of these subscribers are affluent individuals, professionals, and executives. ''We're geared more toward management,'' says Ed Horton, the editor of Denver-based ''Newstrack.'' ''We have a lot of chief executive officers and company presidents.''
In a holiday-shorted summertime week, investors seemed to have some idle time on their hands. So with not much else to do, they listened to rumors. First, there was the rumor that the Federal Reserve was going to tighten the screws on monetary policy. Then there was the rumor that Brazil was about to default on its loans. There was also a rumor that a leader of the Soviet Union had passed on. Except for the monetary policy story, which may or may not prove true this week, the other rumors turned out to be false.
Still, the market seemed more interested in reacting to rumors than facts - like a small drop in unemployment and a rise in the Conference Board's consumer confidence index - and the Dow Jones industrial average fell 18.03 points, closing at 1,207.23.