I don't know if the 375 has a turnbuckle on the inside of the cabin running from the mast to the cabin roof as does the C36MKII. If so, and the turnbuckle is loose, maybe there could be some small amount of motion between the bulkhead and cabin roof...leading to a squeek? The below is a pasted comment from a past post.
 
"Per our surveyor's input- the turnbuckle should be only slightly snugged (just beyound hand tight). The purpose is to stregthen the cabin roof and minimize the hull and cabin roof from "oil canning" from the loads on the hull. Water pressure pushing against the hull sides want to push the cabin roof upwards. The turnbuckle counters this and pulls the cabin roof down. He mentioned old sailing ships incorporated this design to increase strength. On some of the boats we looked at, the turnbuckle had been overtorqued and the topside U bolt nuts were compressing the cabin roof, creating stress cracks and possibly other damage. He pointed out Catalina should have used larger washers, or better yet, a stainless steel plate to spread canin top load- which is what we installed after buying our 36." 

Just a thought.