Update:
In the meant time I ordered replacement bearings and I bought the three Noctua IP67 fans and they have a lot of airflow. In order for them to suck the air through the evaporator unit and not sideways I had to make a construction to make it airtight against the box on the outside. Up till now not a big success.
So today I replaced the bearings of the motor which was quite a challenge since the pulleytool would not fit under the bearing
The low bearing was a no go, the upper bearing I sanded off the pulleytool hooks more flat so they would just fit.
After that it was a piece of cake to remove the first bearing.
The second took me a while with some self made pulleytools which failed but in the end I used two large screwdrivers and wricked it up. It came off eventually.
I mounted the low bearing by using a drillpress which worked great and I made a small alu pipe, mount it in the drillpress and pressed to the upper bearing which also worked quite nicely.
Mounted the motor back and.................... a lot less noise
Maybe not low enough to sleep again (since we are used complete silence by now) but still a very good improvement.
Thanks all for the recommendations and support esp SeanB many thanks, it is much appreciated