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What kind of machine is it? Have you checked the spark plug and exhaust port? Can you pinpoint the noise source area? It's not a gas powered popcorn maker is it? Sorry, couldn't help myself.
Most unusual symptom...
 

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Discussion Starter #3 (Edited)
It's a weed whacker. it's loud popping. it has three choke settings full half and off I tried half and off that did'nt work to stop the popping. so killed it with the button. looked at it nothing was loose waited till it was cool enough to touch the muffler. the exhaust port looked good and there is a port if you remove the carb
 

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Is this perhaps a 4-stroke unit that runs on mix? That would explain the symptom - if so has a cam and/or valve issue.
 

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You never mentioned whether or not it runs on mix, and as usmcgrunt indicates there are 4-strokes out there (they have no crankcase oil reservoir) that do run mix.

You didn't post a model number, so you can't expect exacting answers when you don't provide much information. You didn't post what steps you've taken thus far to try and diagnose it. You can't expect us to be mind readers...

But anyway, I'll give you this gift of information: A 2-stroke popping out the intake although rare, is usually caused by either clogged exhaust (least likely), a cracked or fouled spark plug, or a bad ignition coil or coil wire shorting to ground. I would focus on the ignition system. I suppose even a bad ignition kill switch that's bleeding off coil voltage could cause it. I always isolate the coil from the kill circuit to start off when troubleshooting magneto ignition systems.
 

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Discussion Starter #8
It's ut20772. it does run on a mix. it has 25 cc engine it's a zip start trim'n edge and it says it's from 01 to 03
 

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That may not work. Loctite is designed to release with elevated heat. Blue definitely won't work, red might.

I digress, if a muffler comes loose, often, but not always (probably about 1/2 the time), the thread bosses and screws are damaged. They may not look it, and one easy way to check both the screw and the boss is without the muffler, thread the screws in to about 9/16" deep, and wiggle them. If they wiggle a lot, threads are damaged on either or both of the subject threads (bosses/screws).

I have found that most often replacing the screws is sufficient, but you always have to gauge the condition of both. AND if the muffler bosses (mounting holes) are egged, it's definitely a crap-shoot to re-use it. The reason it came loose is usually from overheating, which can be from a number of problems - mixture too lean (carb. issue or vacuum leak), clogged muffler or port, engine lugging from running with trimmer line too long, ignition timing issue (rare), plugged cooling fins, to name the major issues that crop up.

I think the popping you were hearing is the actual un-muffled sound of a 2-stroke. It does definitely have a pop to it, and if revved-up will make a ratty sound without a muffler.
 
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