Bullfrog taddie good guess, Greenfrog might be also.

If you see any adults look at the eardrum. Bullfrogs have
a fold of skin that curves around the eardrum, in Greenfrogs
it goes down the back. Bullfrogs call is 'rum, rum, rum'
and Greenfrogs, I think, are like the pluck of a banjo string.

k :-)