One problem related to noises during shifting has been reported for the 2001 Toyota Tundra. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2001 Toyota Tundra based on all problems reported for the 2001 Tundra.
My 2001 Tundra, v-6, sr5 access cab truck turned 105,000 miles recently. My transmission started shifting very hard one day. I took the truck and had the transmission fluid changed and it seem to get better for a while, then the overdrive began to make a roar when it would engage. Shifting between gears 1-3 works fine, but when overdrive kicks in, the noise and vibrations occur. I took my truck to multiple transmission repair shops and got the same message. They have seen this issue with Toyota trucks (tundra/sequoia) around 100,000 miles, where the overdrive slips and a bearing must be changed in the transmission, requiring an overhaul.