Vibration/ Low Grinding/ Rattle

[cobrabuilderI]

Gentlemen-
After my post concerning the fuel delivery problem, had something ELSE ---
Picked up my nephew from my sisters house to take him up to my folks for dinner last night. Was all happy my baby was going to be okay with the fuel problem fixed and was running nice. Ran it for 20 mins. to pick him up and then we left and ran it about 15 min. or so, got on straight away after turning corner and I hit it. Took it up to 6 on the tach on each gear to 70 mph then came back down to 55. After I did that and was still on road, when I would engage clutch, or put gears in neutral, there was a sound like grinding- not real bad grinding like when you put it in reverse with it running but like a low grinding/ scraping noise. It only made that noise at higher speeds like 55 mph and then let off. IT was almost like a vibration. At first the noise wasn't bad, but the more I drove it the worse it sounded. Got to my folks ate dinner, and came home, it was doing the same thing. As long as I was running with gears engaged it was fine, which, by the way all the gears worked fine and the clutch worked fine everything worked great except for that noise. Let off the rpm and that noise would start. It hadn't done that before at all. I thought it might be the clutch plate might still be engaged somewhat as I do have a hydraulic clutch that has some adjustment. Any thoughts?