what causes loud patches when driving

[85-m1028]

sometimes when I'm driving "usualy accelerating from a stop" the engine will get really really loud for a couple of seconds and go back to normal??? kind of scary sounds like it's gonna blow up!!!!

[Subzilla]

Could be the fan clutch engaging/disengaging causing the fan to spin more. When my rev up the rpm's, my fan can be pretty loud.

[JDave]

My cold advance sensor had bad contact and would randomly advance the timing. Check the lead I believe mine went to the back of the passenger head.