Static on landline

The gateway had to be replaced recently. I don't use a phone much, but sometime after the gateway was replaced, I noticed on a call that there was a lot of static. I had to keep asking the other person to repeat herself. I thought it was a problem on her end and forgot about it. Now I've noticed the static on several other calls as well. Not every call, but it's noticeable on some. The wifi kept dropping out with the old gateway, and it was determined that it was the problem. I didn't notice until the tech left, that the replacement is a used one with dings and scratches on it. Figured for the amount I pay each month, and how long I've been a customer, I should have gotten a new one. Now I'm wondering if the replacement has issues, too. It's hard for me to try and troubleshoot this myself, since the static doesn't occur on every call. I was hoping someone could give me some advice on what I can look for on my end, maybe with the gateway. I don't want a tech to come out if I don't really need one. Thanks.