Ok, thanks for the reply. I am sorry I couldn't respond earlier. I work in the field during the day and answer questions here at night.
I don't have many of these machines in my area so, I can't say for certain your noise if normal. I do know they have a roar that is different if you are comparing it to a standard drive system.
Since you just got this machine, I would recommend you perform a full service on all the fluids. The manual shows they should be changed every 1000 hours. I would look closest to the Transfer Drive (Hydrostatic) Oil attached to the rear axle. This is a separate compartment and has two plugs on the right side. The bottom one is a drain and the one above it is the level plug. The oil should be level with the threads.
Your machine should have an Owners and Operators manual in the seat back pocket. (OSHA requirement) and this includes all the details for Preventive Maintenance, refill capacities and specific service hour intervals.
If you do not have the OOM manual, I highly recommend you purchase one. It also includes operating tips and identification of all controls.
You can even order it online from www.cattechmanuals.com
Title: SEBU7415-04 902, 906 and 908 Compact Wheel Loaders - Operation & Maintenance Manual
Serial Number: 6ZS1-Up,MER1-Up,7ES1-Up,8BS1-Up,TAR1-Up
If you need more help with this, please let me know. I will be glad to help all I can.