'05 G35x, 29K miles: Yesterday I went out on the road, Between 40-50 MPH it sounded like I was riding on a freshly ground down road (like where they cut grooves when getting ready to repave). But the road was smooth. Couldn't feel the problem in the car or steering wheel. This has happened a couple of times and seems to go away on its own while driving. And sometimes it isn't noisy at all from the getgo.
Info - don't know if this is a factor or not but: Two months ago I had the car in for a "metallic clinking noise when shifting into D or going from R to D" etc. Sounded to me like a sloppy U-joint. The Service Manager said Infiniti had used the wrong lube (somewhere) and they needed to remove 5 (4?) bolts, fill with the proper grease and replace the bolts. I got the impression he was talking about the rear axle. They did whatever and the clinking stopped. I'm wondering if anything they did might be related to this current problem and I'd like to be armed with some info before talking with the service guys again.
Thanks in advance.

 

I am having similar vibration(after clutch install)-just like on rough road. Seems to be car speed, not engine speed dependent.
Flipped through shop manual-it says something about checking prop shaft runout. I knew for sure that it was disconnected on my car and I think it has 4 bolts. Manual calls for proper alignment procedure of prop shaft or it will create vibration. I do not have any vibration in steering wheel.
I am planning trip to transmission shop to check things out.
I could be wrong and it may not apply to your case, but it may be worth mentioning to Infiniti service

 

Your prop shaft disconnect and (mis)alignment theory makes more sense than my guess at the rear axle being worked on. And, like you said, the noise is MPH not RPM dependent. I have a real hot left rear wheel also. Swapped out the rotor and pads yesterday and noticed the piston was hard to reset. I don't think that has anything to do with the "rough noise" squawk though. But it definitely needs fixing ASAP. Thanks for your reply, obender66.

 

Maybe rear axle bearing?

 

I had the caliper replaced today. Fixed the hot wheel problem of course, and the car is running like new. I knew the rotor was a little worn and the pads were totally shot when I replaced them. Maybe the pads caused the noise problem. Never had worn pads cause that kind of ruckus and even if they were the cause it seems unlikely the noise would be intermittent. I dunno. I'll keep the board posted with any new developments; maybe it'll help someone else down the road. I'm thinking of trading it in for a Camry because I'm just getting too old to enjoy working on even easy problems during the weekend. Kinda PO's me 'cause the car is so damned nice. I'd love to get a G37 but can't justify the extra $7,000-9,000 to myself. It's a b**** gettin' old!