I could hear a very loud multiple thud sound under the car on the first gear. on 2001 BMW X5

Multiple thud sound on the first gear only specially when the road is going up. The thud could only heard on the first gear and after that no more. My mechanic said it might be the transfer case, He is charging me too much for this that i can't afford to spend for this old car, please kindly help or any suggestion. Can you tell me if the mech.is right, Thanks in advanced.

by in West Covina, CA on May 28, 2012
1 answer
ANSWER by on February 14, 2013
Do you get any warning messages? Check engine light on? It could be a different problem so you may want to get a second opinion.