Isolating AM Radio Whine

Hello, all,

I am trying to eliminate a particularly annoying engine whine I am encountering on the AM band.

Vehicle is a 1997 S-10 with the 4.3 V6. Sound system is all stock (factory AM/FM/CD player) with speakers in dash and doors. The noise only occurs on the AM band, and is most prominent around 740 AM (my favorite local news talk station, natch). The intensity of the whine increases when going under overpasses. Originally, it seemed as if it was only occurring during daylight hours, but yesterday I determined that, in fact, it only occurs when the headlights are OFF (and the daytime running lights are ON). The whine goes away when I switch the headlights on.

Anyone ever heard of this sort of thing being caused by the DRLs and/or associated circuitry? I have already eliminated many of the usual suspects (cleaned & replaced battery grounds to frame and body, replaced worn alternator and battery, checked integrity of antenna connections & grounds).

Thanks in advance for any suggestions / observations.

these vehicles consistently had antenna problems...pull the radio and plug in another antenna and take it for a quick drive... it it sounds fine you have to replace the antenna....  take a day off work to get the job done.....

and yes it could be a module issue... i spent half a day a year or so ago dealing with a radio concern on a Buick Roadmaster that turned out to be a bum DRL module.....

Thanks for the response, Kevin.

I have already replaced the antenna, swapping it out with a known good antenna from a 1999 S-10. Noise still there. Do I also need to check/replace the section of antenna lead that runs from the radio to the engine compartment?

I have pulled the DRL fuse, and still I get the same noise. The only time the noise goes away is when I turn on the headlights. I am assuming that the DRL fuse does not directly provide power to the DRL module, and, as such, when removed will not necessarily de-activate the DRL module.

I am not looking forward to trying to get at that module, which appears to be located above the steering column.

Thanks again for any information.