i have noticed for the last few months when i have my climate control on either recurculate or fresh air i have an ocasional sound. it sounds like a cicada bug is living in my truck. i have noticed it will stop when i let off the gas and it doesn't seem to happen all the time or to be repeatable with the same conditions. any one have an idea as to what it maybe. i have made sure to keep all the trash off of the air intake behind the hood.