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.
It’s “Case of the Phantom Frog” by E. W. Hildick. 🙂
I think the previous comment is correct. It’s The Case of the Phantom Frog by E. W. Hildick. It’s part of the McGurk mystery series.
https://jestressforgottenstories.com/2024/09/21/the-case-of-the-phantom-frog/
An elderly woman has been looking after her nephew’s young son, Bela, because his parents were injured in a car crash, and they’re in the hospital. Bela is from Hungary, and since he came to stay with her, odd things have been happening. She keeps hearing loud frog croaking at night, after Bela goes to bed. Bela insists that he doesn’t hear anything, but his great-aunt is afraid of frogs, and the creepy croaking is driving her crazy! Since a phantom frog is hardly a police matter, she hires the kids from the McGurk Organization to “babysit” Bela and see if they can figure out where the frog sounds are coming from. The kids also find it difficult to locate the source of the croaking at first, but they’re pretty sure Bela is responsible for it. They consider whether Bela could be some kind of werefrog (like a werewolf, only green and hoppy) or if this is someone part of an elaborate prank because Bela isn’t happy staying with his aunt. As you said, though, it turns out that Bela has a secret pet frog. He’s had it since before he came to the US, and he loves his frog. Because his aunt can’t stand frogs, he was afraid she would make him get rid of it, so he’s been hiding it from her. He only brings it out at night, so she won’t know. When the others realize what the situation is, they talk to the aunt, and she agrees that Bela can keep his pet. The others make a special enclosure for it so it can’t get loose.