i have a 2000 ford f250 and since i have put a ts performance 6 pos. chip on my truck every morning that its cold or night 30 to 50 degrees outside at about 1,500 rpm or so my truck makes this loud kinda like a jet engine noise out the exhaust but if i give it more gas or let off the gas it goes away. ive been told by mechanic's not to worry about it but its kinda annoying to hear. i've noticed on warmer days where its like 70 to 100 degrees out it doesnt do it. anyone have any ideas on what this might be? thanks for yall's input on this.