My FM stations are fine, but I get engine noise (to the extent that I can't hear anything) when I listen to AM stations (I hate missing Prairie Home Companion!). What's the fix?

If this just started, check your antenna connections. Next, if this is an older style Telescoping antenna, be sure it is fully extended.

Be sure both radio and antenna have a GOOD ground to the chassis. A bad ground might let the radio operate but allow it to be noisy.

Thanks Walks On Water! I think my problem's the ground. I'll check it out next weekend (too busy this weekend).

You may also have some "leaks" in your ignition system.

My learned friend, TCM, has also has a good point. Bad plugs and wires. Sometimes just a good tune-up will quiet you radio. Not being able to hear the sounds makes if difficult to judge.

My favoite way to check an ignition problem on my cars was by tuning between stations on the AM radio as I pulled the wires off the plugs. One most use caution though as it will get your attention very quickly. We were doing this on my son's race car. When he was checking, he pull one off and got it between his hand and his--- let's just say his crotch. Hadn't seen that look on his face sence his wife told him see was pregnant with their fourth.

Is it a loud crackling or poping sound- plugs wires or distributor.

Is it a "Wining" sound- alternator.

All these are just possibilities.

I had a similar prob a few years back I solved it by replacing the HT cables (cheap.) It was a cracked HT cable causing a small "tracking" effect (could only be seen when there was no light) also the plug caps if you have to assemble it (Motor factors sell them preassembled)
consider also changing sparking plugs
I recommend getting NGK/ Nippondenso or Bosch brand plugs because they are good with keeping "RF" noise down
And check this page out has in it how and where RF noise occurs:
www.centuryperformance.com/spark.htm