eliminating overtones

[mif]

I have a set of Toca custom deluxe congas. I am having a heck of a time getting rid of annoying overtones on the conga. So far I have:
1. replaced the head with a more uniform and thicker skin.
2. treated the tuned head with pure lanolin
3. made sure each lug zone of head is tuned identically - (even if one lug is torqued more or less than the next)

STILL I GET THIS ANNOYING RING WITH AN OPEN TONE SHOT. HELP!!!

[Mike]

Nasty overtones often occur with too tight skins.
But also water buffalo hides are known for unpleasant side effects.
Some congueros place sticky tape below the head to dampen overtones.

[Mike]

Another thing is: Synthetic heads promise to eliminate overtones... Well, still not my cup of tea (see earlier posts), but worth trying, sure.
By the way, my LP Classic quinto has these overtones, but I can live with them.