When toilet is flushed, tub drain sounds like there is draining in to a hollow barrel.

There is probably a P-Trap missing under the tub. Check it out and let us know. Back to you. Milo

There is probably a P-Trap missing under the tub. Check it out and let us know. Back to you. Milo

Thanks Milo. I am unable to get under tub, but I closed the tub drain in the tub, flushed toilet and all sounds normal. Now what? Thanks.

Hi 89 and welcome to The Plumbing Page at AskMeHelpDesk.com
I have a different take then Milo. Milo thinks there might not be a tub trap while I think that's where the sounds coming from. Let me explain.
Vents are there to relieve suction caused by draining water, If a vent's blocked the suction has to relieve itself some where, In your case the tub trap. The sound you hear is the suction being pulled through the water in the trap. Your solution would be to snake and clear the bathroom vent. Good luck, Tom

Hi 89 and welcome to The Plumbing Page at AskMeHelpDesk.com
I have a different take then Milo. Milo thinks there might not be a tub trap while I think that's where the sounds coming from. Let me explain.
Vents are there to relieve suction caused by draining water, If a vent's blocked the suction has to relieve itself some where, In your case the tub trap. The sound you hear is the suction being pulled through the water in the trap. Your solution would be to snake and clear the bathroom vent. Good luck, Tom

Thanks Tom. Will get someone to snake vent and see what happens. Will let you know.

Please let me know if that helped. Good luck, Tom