Suddenly I have a whirring noise coming from (I think) my alternator, and the smell of burning rubber/plastic underhood. No idiot lights are lit. I'm suspecting a burned rectifier or diode, which would surprise me since my car has "only" 160K and I've put nearly 300K on a similar Accord with no alternator problems of any kind.

Earlier this year I installed an Interstate battery; could an internal defect in the battery have caused this? What's the best way to go about diagnosing the source of the problem? A new Denso alternator is pricey ($265) so I want to make sure I get the problem corrected the first time, and don't fry a new alternator.

Many thanks for any help!

 

The whirring sound might be from a bad bearing in the alternator. Check the drive belts for excessive wear and proper tension as that may be the source of the burning smell. I don't have the spec on this, so you should verify the slack with a Honda shop manual or a reputable mechanic.

 

you might try putting a long wrench or metal object on the alternator surface and putting your ear up to it, it will magnify any sound coming from it. Ive done this before with alternators that were failing and heard unhealthy sounds from the wrench. Don't get the wrench stuck in a belt

I installed a alternator from advanceauto on my 96 accord about a year ago it was right around $90 after coupons and cashback from affiliate sites.

 

Hmmm. Well, the noise has stopped and there's no more smell. Alternator light isn't on, battery seems to be charging OK. Maybe just a "fluke"?

I'll put a voltmeter on it this weekend and see what I get. Worst case scenario is I need an alternator; a rebuilt Denso is about $165 at NAPA with a lifetime warranty, and it's easy to change.