My 2001 Honda Accord EX was due for a timing belt change and my favorite automotive shop, not the dealer, performed this task on 10 August 2009, and included replacing the two serpentine belts, balancing belt, and the water pump.

On around 17 August I detected a low vibrating sound emanating from the serpentine and timing belt locations in the engine compartment.

This sound is not present after the engine is started and idling but becomes audible at idle after driving for a few minutes--the sound (vibration, rubbing, whirring???) is not loud but becomes obvious when opening the hood at idle. It does not go away with continued driving and idling.

The technician who performed the work stated that the sound would disappear after putting 500 miles on the car to “work” the belts in, so to speak.

However, after driving more than 500 miles the sound is showing no signs of going away.

Any input is greatly appreciated -- thanks in advance!

 

For me, I'd describe the sound of a NEW timing belt, maybe a tad over-tightened, as a whining sound. But sounds are really tough to figure out on-line...

A low vibrating sound reminds me of a loose belt. Maybe only after it gets hot? Watch the external drive belts to see whether they're vibrating. If not, then check (or have the mechanic check) for loose timing belts.

Check out the sticky-thread at the top of this section, something about 'timing belt tensioner warning'. Would your mechanic be offended if you printed that & showed it to him?

 

I've seen/heard lots of overtightened counterbalance belts make a whirring noise.
That's my bestest guess.