Front end noise

[fuzzy93]

I have a 2001 Avalon XLS w/ 88,000 miles. I occasionally get a noise from the engine compartment/front end. It sounds like a bucket of bolts.
It happens for short periods of time, whether the engine is cold or hot, seemingly mostly at low speeds and then stops.
Any thoughts?

[silverxls]

could possibly be pre-ignition, commonly called pinging. try buying gas from a different place, or using plus gas or premium and see if it goes away.