From season 4 of The Flintstones:
Fred (Alan Reed) forms a barbershop quartet, but there's a problem. Barney (Mel Blanc) can only carry a tune singing in the tub. The newly formed Flintstone Canaries land a deal to do a commercial jingle, and, well, it doesn't end well........!
To give you some idea, here's the audition:
Henry Corden, who'd later be the full-time voice for Fred, reportedly did the singing in place of Reed. Blanc, on the other hand, had plenty of experience, having done some in-character numbers for Warner Bros. (Bugs Bunny, Daffy Duck, et al). Shoot, for all we know, he could've released an album or two that'd be a collector's item today!