Most likely, this is a motor mount problem which can be costly but shouldn't be if you have a trustworthy mechanic.
Worn steering or suspension parts. This can be very dangerous, so have this repaired ASAP.
The root is part of hair embedded in the follicle in dermis. It has an attached smooth muscle which can contract causing the hair to stand up right. This causes the skin to form a slight bump which we call a 'goose bump'.
You need a steering stabalizer and if you have one it may need to be replaced.
it may be a serois medical conditiion, ask a vet. is the rat old? is the bump big? is the lump swollen? is the bump on a patch of thin skin? where has your rat been? is the bump smooth or scaly or something else?
your spine ya dummie
It might be Syphilis.
suspension your steering dampner has gone bad, replace it and the shaking will stop.
When you hit the bump, the mouse wakes up.
appulse, bang, blow, bounce, brunt, buffet, bump, clash, concussion, contact, crash, crunch, crush, encounter, hit, impingement, jar, jolt, jounce, kick, knock, meeting, percussion, pound, punch, quake, quiver, ram, rap, rock, shake, shock, slap, smash, smashup, strike, stroke, thump, tremble, tremor, wallop
check shocks
The higher the temperature, the more the molecules shake and bump into each other.
the bump after you get stung or bitten is caused by your body's immune system isolating the poison so it won't get into your blood stream