dull hum noise from exhaust at idle in Park
My '88 is in storage at a friends garage. It's been about 6 months since the car was last started. Car is connected to a Battery Tender and has Stabilze gas treatment in the tank.
Today I went to start it up - started just fine. Throttle had a slight hesitation, so i just let it idle while I cleaned the car up. After letting it idle for about 20 min, I starting hearing an odd hum noise from the rear - and more specifically out the exhaust pipes. Up near the engine all sounded fine.
I let the car idle for about 25 min, so it could warm up, then shut it down. Checked things over - all looked fine. Started the car right up again, and within a few minutes, the hum sound was back.
I didn't drive the car - I hope to tomorrow.
Any ideas what the hum/drone like sound could be?
Some info on the car: 1988 Corvette, auto, all stock, 68K miles. Has the muffler eliminator exhaust system (no mufflers). Has all the cats. Over the years I have always thought the cats may be getting clogged...
Suggestion, comments welcome!