What was that?!

[mxfever090]

I bought my truck from my dad with 56,000 miles on it. I was recently talking to him about the last service and he asked me if I ever heard something that sounds like a smack under the hood after it starts? I hadn't and didn't think anything of it. Two weeks ago the family jumped in the truck to come home and I fired it up. BAM! Sounded like someone punched the firewall! The wife even said "what the h@#* was that?" I jumped out and looked under the hood and saw nothing. Truck ran fine. Well today at lunch it did it again but this time I could feel it in the floor. Any ideas? Still runs fine and can't find anything out of the norm.

[kuntryquesttsi]

Is your trans loose? or motor mounts? causing it every now and then to rock into the body?

[mxfever090]

I did check the engine mounts and they are ok. But for some reason I didn't think about the transmission mount. I'll check that one out next. Thanks!

[kuntryquesttsi]

Also I see your sig says 4x4 check your axle from the transfer case and the transfer case itself. anything that could move on a decent start.

[bens99f350]

mine does that occasionally - I think it's the vacuum pump doing it