I smell something burning...

1) Thru heater vents while sitting at long stop lights.

2) In my garage after turning off engine and walking beside car to go into kitchen.

I don't see any fluid leaking on exhaust pipes.

I don't see any smoke.

I can't determine exact location of smell. Just under hood -- somewhere?

Any ideas?

Slipping timing belt?

Slipping serpentine belt?

1993 EX 4 speed automatic