Our downstairs toilet appears to be air locked and makes a rumbling sound.toilet flushes fine however when we turn on the bathroom tap upstairs the sound stops.we are on city water and our home is 29 yrs old.any suggestions on how to stop this noise it's been about a month now thanks

When do you heard that noise and how long does it last?

No such thing as a plumbing air lock. What you hear is a vibrating washer in either the toilet fill valve or the stop valve under the toilet tank.
What kind of fill valve do you have?