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From what you have described to me its definately a problem with the tonneau motor due to the grinding noise you are hearing. Essentially the motors teeth skip and it goes out of synchronisation causing it to go haywire.
Now where to from here.
There are 2 possibilities here. The first is the motor is made of alloy and they can bend causing the teeth of the motor to not engage correctly causing the grinding noise. The remedy is that Saab released a re inforcement kit for this problem and often fitting this re inforcement kit and straightening motor is all that is required to rectify the problem.
The second possible outcome is that the re inforcement kit is already fitted and has not alleviated the problem, or the teeth are stripped or damaged from skipping teeth too many times. Its advised at that point to replace the tonneau motor.
They are quite expensive new (check with your local saab dealer) but Im sure one can be located 2nd hand in good condition.
They in reality are best fitted by saab specialists as they often need to be reprogrammed (They have potentiometers inside) with Saab special equipment.
If you have any more questions feel free to ask.
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