Sorry to disappoint you mate but most if not all window a/c's are noisy due to its compact design. The a/c's compressor is the culprit, this is the one thats creating most of the annoying noise you hear.

For utmost convenience and superb quite performance the high-wall or mini-split type would be the most practical option. I don't know what type of "Technical difficulties" your repairman have encountered but I highly suggest that you have a chat with other reputable a/c technicians.

Please let me know what are the "technical difficulties" I may help you.

Cheers,