>>Is this standard for a computer of this age
>>are these problems fixable?
Assuming no hardware problems : yes.
>> do not want to take it back to the place that just did the motherboard (because they gave it back to me making this horrible noise).
Nonetheless, that is what I would do. Ask them to explain why it does this now, and didn't before they repaired it. If they say that it's a software problem, have them show you exactly why they think that.
The Apple store may well be able to do the same, and at the very least tell you if the noise is 'just' loud fans, and if so, if the cause is a 'busy' computer due to running software, or because a sensor wasn't reconnected and the system thinks it's getting really hot.