2001 TJ Unidentified Banging Noise from Front

Took the rig off road in February for the first time in it's life (bought it fresh from a road-only user) and now it has an unidentified banging noise coming from the front. It only happens on a cold morning at straight take off (no warm up) and although the banging sound is soft but increases in speed as I speed up. I can feel it through the pedals and firewall but not through the clutch or gear shift. After about 30 seconds, it stops altogether. I have tried warming the engine for 30 or more seconds in the morning before take off and there is no sound at all when I do this. Some mornings when it's warmer and less damp, there is no banging sound at all at start up. I thought this might have something to do with the radiator or some sort of expansion with fluids when everything is cycling through at start up but a friend says this is doubtful. This only occurs at first start up, not at any subsequent start ups during the day. The sound is not constant during drive and only happens as above. It does not affect the performance or handling but it is strong enough to feel in the cabin.
I had Jax's look at it but they couldn't hear it and I suspect because I took it to them warm, there was no way of replicating the sound unless I left it there overnight (not an option).
Any ideas?

My 97 TJ auto has just began the same story/noise. Had it parked overnight at tha diff place, it went for midnight run as well, but NO noise in the a.m. at all. Just comes in intermittently now and then only on morning starts, but disappears after about 1K or less??.....................

Dont know if its the same issue but last saturday I scraped the underbelly of my JK on some rocks at Mt Airlee. Result being a bent bash plate under the transfercase. Under the circumstances where the engine vibrates a bit more than usual like cold starts or when driving close to 3500 RPMs the exhaust vibrates and bangs against the bash plate. Gonna bash the bash plate into shape again and hopefully the noise will go away.

Mani

Thanks Mani, sounds like a possible culprit..will have a look under it.

Did you check the front muffler/exhaust mount rubber, another little culpruit found......... Helps resonnate the underbelly sounds, mine was very loose................