pdx05470

2005 LX470, 75,000 miles. Recently acquired from original meticulous owner who babied the rig and regularly service at local dealer.

I am trying to determine the cause of a rotational low-pitch "helicopter" or "whirling" sound that was first heard and is now most prominent on new, smooth black top at speeds of approximately 45mph and above, but can now be heard occasionally at lower speeds around town. The sound is not a "classic" wheel bearing or differential sound and seems to vary most with type of pavement, although now seems to be ever present. The tires seem to roll smooth without any vibration or abnormal bounce.

Checked by 2 independent, experienced land cruiser mechanics: they think that drive train, wheel bearings and axles are OK and are not causing the sound. No change after lube.
All 4 tires (Michelin LTX M/S, P275/60/R18, with about 45,000 miles over 3.5 yrs) with similar, increased wear on inner approximately 1/4 of tread compared to rest of tire. Records suggest that tires were rotated regularly. Alignment check at an excellent independent alignment/suspension shop at time of purchase showed that alignment was "perfect" and that suspension looked OK.
Local tire dealer thinks that the sound may be from "cupped" tires, although he has not yet had a chance to examine the tires closely.

My question: has anyone experienced similar symmetric abnormal wear (or edge "cupping" on all 4 tires from anything other than misalignment?

I realize that I do not yet have all the information you might need to assist me: are the tires simply worn due to misalignment or are they really "cupped".

My reading suggests that worn suspension components can lead to "cupping", however I think that it is more typical for a single tire or 2 to be affected and not all 4's in a very even fashion unless regular tire rotation is a contributor.

I am hoping that it is not a result of problems with the LX's active suspension system (which otherwise seems to be working OK).

Thanks in advance for your thoughts.