Hi,
Some of you may recall that I posted a message about my "Noisy Frontier" a few weeks ago. The problem was that at about 1000 to 1200 rpm, the cabin is very noisy. However, under 1000 rpm or about 1200 rpm, noise level is very normal. This problem is very noticable during "warm-up" on cold weather days. People suggested I check the heat shield and the muffler. I did both. I didn't find any heat shield problem, and I couldn't feel any leakage from the muffler and exhaust pipes.
What is strange is that when I am standing outside the truck, I don't hear the noise. But if I am inside the cabin, I hear it. I think it's caused by something vibrating. Can it be a problem with engine mount? or a structure problem? The truck has been hit a few times (by the previous owner). Any suggestion?