Re: unexplained lump in rear bumper tread?
Can't tell you why it popped out but I'd bet one the plastic wedge type clips pulled out of the hole in the metal bumper. You may be able to reach up into the bottom to feel whether it just raised straight up or is off to the side of the hole. From the top side you might trying to push down gently to feel where the clip is and once you find it push straight down to see if it'll engage the hole in the bumper. I changed the one on my 2004 because it was all scratched up by the previous owner and it's just held on with square/rectangular plastic clips through the bumper.
2004 Tundra V8 Limited Access Cab 4X4, HANKOOK DynoPro,ATM P265/70R17 113T, Auto Dim Comp/Temp Mirror, Aero Turbine #2525 muffler, Access Roll Up Cover, Optima D31A battery, Eclipse AVN5510]
If a combo of all these whizz bangs met their claims you'd have to siphon gas out of your tank every second day and sell the excess horsepower on the third????
If your engine doesn't consume ANY oil it will seize???