Funny clutch grinding

Hello, question to the original stones For a short time I drive a Grand Vitara Diesel, Bj 2005 170 000 km Now there is a problem with the power transmission. When accelerating from the 3rd gear and a speed from 2200 rpm the clutch grinds, the speed rises to about 2500, — you go from the gas, — then the drive catches again, sinks to 2500 and you accelerate normally further to the next switching point! No matter if 2WD or 4WD. That even works uphill with 2t attachments load! the clutch should be constantly grinding?? What is the cause or how can you explain it? Thank you for your help, I can’t explain it to myself.