I know the feeling of losing your truck to stupid stuff that should not be happening. I had to drive a rental Chevy Metro for a total of eight days over a two-week period. I noticed the manifold noise around 22k, but I'm sure I had it for longer. This will not hurt your truck if you don't let it get real bad. I took mine in three times because of my dealership.
I advise a couple of things on this problem.
(1) Drive another Tundra-that's how I was 100% on my exh leak.
(2) INSIST the dealer check both sides-More than one truck has had problems with both sides. And my dealer fixed the wrong side and gave back to me-noise intact
(3) When you take truck in, Make the person helping you hear the noise-drive them around if you have to.-That way they have to acknowledge the problem.
(4) Check fix-After three days of new manifold, my truck started popping REALLY loud after about three to five minutes after I shut the truck off.-Took back to dealer and they replaced the NEW manifold with another NEW manifold. after that the truck is fine.
The bottom line in my opinion is this definitely should not be happening. This is a major pain in the *** fix. I lost more than a few hours of work and had to drive a 1.8 liter go-cart for awhile. GOOD LUCK ON YOU FIXES AND FEEL FREE TO DROP ME A LINE.