Toilet chugs

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I have an older home and i think the toilet air pipe may have junk/maybe bird nest? in it .Everytime it flushes it makes that "chug chug" noise at end of flush and i hear it a bit from tub drain also. Drain lines are ok as i have cleared them.
What could this be?

 

[hj]

vent

That is one sound that a plugged vent could create. Just do not blame it for poor flushing or drainage.