I thought I'd ask here, cos we gstwinners know everything.
HVAC unit in my house makes horrible noise at start up and is very loud and makes the house feel like its in an earthquake. Its 13 yrs old, but it really should not, cos the other unit does not make any noise really, its quieter than a fan. Its done so for 2 years. I feel its getting worse, but maybe cos I didn't hear it all summer. Only when its heating, not when its cooling.

In spite of this, it works fine. I am thinking its a fan bearing or something simple.

Cool.
Buddha.

does the exterior unit make the noise, the interior (attic) unit, or is is a mobile-home style "package Unit"?

If its the outside unit, it could be the compressor packing it in, which is a difficult fix. That generally makes crazy amounts of noise before it expires. The cooling fan on top of the unit does occasionally die in such a way, however I'm unsure whether it would be effected more by the heat as opposed to the cooling. . .

The interior unit, could be the the internal blower missing a weight, however I think it would make the noise at all settings.

A package unit is a crap-shoot to me.

DISCLAIMER: I'm not a certified AC Tech, however I did work alongside them for nearly two years as a warehouse/shop/general lackey. If its too big of a concern, I higly recommend contacting a GOOD, TRUSTWORTHY, AC company.

What type of system you got?
We have a forced air/gas heat, and were getting a loud, 'moaning' sound. We called it our house ghost. People told us it was air in the gas lines. We had the utility co come out, and...
Turns out, we have an electric humidfier (think: slow moving wheel that dips into a filled pan of water, on the side of the main air duct) that was in need of some oil. Too much friction between the wheel and the holder.

Never would've guessed that in a million years! Loudest thing you ever heard. 

Its the unit in the attic. Outside unit also makes a rhythmic noise on occasion but only when cooling. No worries about it for 6 months now LOL.  Anyway the blower fan seems to be the culprit. Its a fasco A200.

But on the trustworthiness of HVAC mech's I've found that its like looking for an honest politician or a coherent crack addict. I'm pretty sure somewhere in the world, they do exist, but I doubt we will find any around here.

Cool.
Buddha.

check with the local sears. they usually have a list of competent HVAC contractors on hand. i remember when you had problems with leaks a few years back.
Aaron

during heat or cool?


if heat, the cycle pattern is "thermostat on" > "draft inducer motor on" > " gas on " > "ignitor on" > "gas lit" > (if not go to step 1) then "blower motor on"



Cooling:  "draft inducer on" (spins up for 5 seconds), "cooling evap fan on", blower on

Its the draft inducer fan. Replacement is on its way.
Lets hope it fix the issue.
It seems to spin up by hand just fine and not do much other tha nfeel a wee bit out of balance. Which explains why it run 2+ yrs that way.
Cool.
Buddha.

The good news is that after it's fixed, for a few weeks, it'll be like a dream! You'll keep wondering where the sound went.
We had a bathroom door that wouldn't shut properly for about 3 weeks. After I fixed it, it's like heaven! Everytime that door shuts properly now is like a gift.

Nothing like a fixed thing that was once broken for a little perspective on life.

Naaa I'll still be a bit upset that I had to toss a fan that wasn't completely dead.
Just kidding, 2 yrs is plenty.
Cool.
Buddha.

Idea for you Buddha! .. wire up old fan in the yard somewhere...  start it up. .. throw various stuff at it. ... film the action! "Will it slice... ?" .  Viral YouTube fame!

in my case the draft inducer motor didnt die, its blades disintegrated and it wasnt exhausting the hot gases out properly, and the heat exchanger cracked (which was under warranty). so we had to replace the heat exchanger + the draft inducer motor..
There is a safety that kicks in if it detects the flames / gasses on the heat exchanger side (CO monitor i believe).


The trigger is that the blower will keep running (so you will blow cold air) but the heat wont come on as teh safety turns on. You have to bypass it, but its a safety issue so you dont bypass it.

Hvac ( and microwave ovens) are the only things id consider a service plan on. house im in now my grandfather put CHA in and got an open ended service plan on. 30 years ago. its been repaired many times. finally it went .  tech said DAYAMN this is older than me. so they put in a new unit. free. and microwaves lol same type policy. had a vintage microwave  it died after 15 years nearly. replaced sans charge.
Aaron

Well the replacement is spinning better than the one in there now when spun by hand. So I guess it is bad even though it still spun.
Cool.
Buddha.