4x4 is making a hard thump every now and then while in 4hi. Did a search and read most other problems dont think it is a IWE solenoid problem. It does engage and then while driveing it will thump hard every so often only seem to do it in 4hi. Any suggestons on what it is before I take it in. Runs fine in 2wd no problems at all. It is a 2005 STX 4x4 on the floor.