99 Accord with 70k on it (yes 70k - driven by 80 year old). Auto transmission.
Front passenger side there is a deep cyclic noise (sounds like rug, rug, rug...). Noise starts at 25-30 MPH, continues when the car is moving, but in neutral. Noise gets louder at higher speeds, but is not terrible. I suspected tires, but rotation and balance revealed nothing and changed nothing. Suspension feels tight, springs have no evident cracks. CV boots are intact. Turning sharply while in motion, does not increase or decrease noise.
Trany fluid is full and looks good. But noise does not stop in neutral, so I don't think its trany.
No noise in park revving engine.
No evident noise from brakes.
Any ideas?

 

Wheel bearing? I myself have not heard of many wheel bearings go bad on Hondas in General, but with all ofther options exhausted (kind of) a bad wheel bearing could be the culprit.

 

Wheel bearings tend to go bad more often than not when the axle nut is overtorqued. You need to jack up that side and spin the wheel or spin the rotor with the wheel off is a little bit better and compared to what the other side sounds like. It should sound the same. Keep in mind this is harder to spot the noise than when the wheel is on the ground and the car is in motion, but you should be able to tell the wheel doesn't spin as freely as the other side. If it's really really bad there will be play in the bearing and you should be able to see the play versus the other side.

 

Adding to holmesnmanny statement. If you jack up the left front OR right front wheel so it is off the ground, turn the engine on and place the car in gear you may be able to hear if one wheel is louder than the other. If one side is louder, unstake the stub axle nut, loosen it, and retorque the nut to the correct setting, this will reduce the amount of noise coming from the wheel, but the bearing will still need to be replaced.

Prior to replacing the wheel bearings on my '97 I was getting an annoying brake growl/howl/knockback. The car had ~150Kmiles and IMO by 100K miles the bearings are probably worn enough to warrant replacement. Loosened the nut, retorqued it which removed the growl and pad knockback, but the bearing was shot(still sounded like sand).