When I accelerate beyond 80 km/h grinding is felt as if car is dragging or working hard to accelerate and is immediately gone on removing foot from accelerator or putting gears in normal. Car has done 1000 km after engine overhaul and I noticed this first time after completing running on rebuild engine. Before engine overhaul I was driving car up to 110 km/h and there was no such feeling/sound. I also noticed a long rubber boot on left side of steering rod that connects to end, worn out.
It might be the wheel bearings. But it can be gear box issue, as you are saying that the grinding noise is there when the car is in gears. You should first check with gear oil.
Sent from my LG-F400L using Tapatalk
If boot is leaking greas the need to changed with new greas, other wise it's ok.
Check your engine shields, wheels shield and belts
The same happend with me 6 months ago, i thought its due to tyres so i changed all four tyres, but the prob still existed, then i came to know its bearing problem, then i changed bearing and problem solved. so would suggest to check wheel bearings.