Yamaha Clavinova CVP-50

Every C# with each of four half steps descending makes loud noise.
Every F# with each of two half steps ascending makes loud noise
Otherwise, all of the notes work well. Any ideas on repair?

This could be a combination between bad rubber contacts, corroded contact circuit boards (MK) or maybe one of the connecting cables

I just wanted to post to let the forum know that I found the problem. A previous technician had taken the keyboard assembly apart and reinstalled the rubber strip backwards. The rubber keystrip was original to the piano, so I ordered a new one from Syntaur and it worked great.