This was a book on cassette – it may have had an accompanying read along book.  I checked it out from the library all the time in the mid to late 90’s.

There was a group of kid detectives who were asked in to investigate strange noises in an old house and prove it wasn’t haunted. There was a sick, bedridden boy visiting the owner of the house. After investigating, the detectives found that the sick boy had a secret pet frog that was causing the spooky sounds. The sick boy might have been visiting from a different country.