I assure you, it's...BEETLEBAUM!!!!
Why not Beetle Bomb? I believe Spike Jones was making a funny allusion to a Beetle-something-or-other already known to his listeners in his day--and that would have to be Beetle
Bomb. (Beetle Bomb was the name of a rather famous Grumman F8F Bearcat that flew with the Blue Angels shortly after WWII.)
BTW, if you listen carefully to the Spike Jones recording, I think you will discover that he does not pronounce it
baum, but
bomb.
Furthermore, Jones mentions a P-38 in his comical story of the race. (A P-38 was a fast pursuit
airplane--which is an aeronautical allusion, just like the name Beetle Bomb itself.)