I recently test drove the factory 3 wheeler demo and found it to be great fun.
My question before I decide to buy is about an awful squawky noise which the sales guy said they all do and claimed it to be caused by some kind of diff setup, it sounds more like a bit of grit can sound when stuck in a disc brake or a dry bearing.
Do they all have this problem? (it wasn't the belt slipping) I enjoyed the rawness of the drive but not this noise.
If it resembles a high pitched chirping noise then perhaps it is the belt rubbing against the rear sprocket. The bevel box gives out a whine as it's attached directly to the frame, or was on the older models. The chirping noise will vary between acceleration, deceleration and coasting, which helps to narrow it down.
It can be horribly distracting as it can feel like something wants to drill through your inner ear real bad!
I started this post a few days ago:
Belt Noise 
