I noticed a crackling sound in the 7000 to redline rpm range a few months ago. It would come and go. I took my car in today for regular service and inquired about it. They said it was due to air bubbles in the radiator lines and will not pose a problem. They topped up the coolant and sent me on my way.

Anyone else have this happen to them and if so did you have the same results (advice from mechanic)?

 

I may be suffering from this to. Mine sounds quite bad though. Sometimes can sound like the engine is going to explode. Mechanic at the dealer says he has no idea what the noise is and that he could spend hours and hours dismantling stuff to find the problem and still be none the wiser. Second time ive taken it there. May try a different dealer. The mechanics there seem to be clueless! Let me know if you resolve yours.

 

If it continues to happen you may have a leak in your coolant lines. The crackling like you said is due to air being trapped inside of the lines. The car eventually rids itself of this air as long as the radiator is properly sealed, however, any leaks could keep the problem coming back. This is a typical noise when doing a full flush of coolant and a refill. One would remedy this by driving the car for a few hours, then coming back and topping off the fluid which would be lower due to the removal of air from the system.