I play the violin, and for some reason, especially when I go from the A-string to the E-string, the E string squeaks a really high-pitched note that sounds like a harmonic, even when I take all my fingers off the fingerboard. Is there any way to stop this from happening?
Speaking as a fellow violinist, this is a common problem. It only happens on the open E string and it often comes when low bow pressure is used usually combined with a shallow angle between bow and string.
The standard solution is to play 4th finger on the A string, particularly for intermediates on up. If you are a beginner use it as an excuse to get practice using your 4th finger. In other words, try and work around it.
There are times, though, when the open E string can't be avoided. A double stop would be a very obvious example. In that case use a bit of extra bow pressure to snuff it out.
In general playing if you feel you need the sound of the E string for an open E then make sure you approach the stroke with a good bow angle and reasonable pressure.
Frustration often leads violinists to try different brands of E string to try and find one which doesn't do this. When violinists get together for a chat they will often compare notes about which strings they use and say things like "I use brand B for my G, D and A and brand C for the E".
I've never found a violinist who has found the secret of which brand of strings guarantees no whistle on the open E but feel free to join in the game. Meanwhile try a bit more bow pressure and a steeper bow angle.
Edit: Augustin Hadelich has a YouTube video talking about this problem and showing that even top soloists have this problem:
His diagnosis of the problem is that it can arise when the bow doesn't "catch" the string well enough.
Augustin Hadelich's video in Brian Towers' answer is useful. I would expand on it a little:
- The most sure-fire way to eliminate this problem is to use an E string designed to eliminate whistling. I've used this "Kaplan Solutions" E (https://www.sharmusic.com/Strings/Violin-Strings/Kaplan-Violin-E-String---4-4-size---Medium-Gauge.axd) at various times of my life and whistled maybe a couple of times per year. The tradeoff is that other brands offer a more "brilliant," incisive E tone, especially desirable for a soloist to project above an orchestra. But if you're in a place where avoiding E whistles is more important than being a connoisseur of string tones, then it's a miracle cure.
- If you have to use an E that whistles, there are still a few bow-hand tricks you can use. The important thing is to let the bow hair get a good "grip" on the string before setting it in motion. This is key to good articulation at any time, but especially important here.
- If you're simply going from an A string note to an E string note, you can get a good articulation by engaging the fingers of the bow hand; does a good job of showing off the "squeeze/extend" motion that can give a cleanly articulated start to any up-bow or down-bow.
- If you're playing a chord that has open E on top, your options are more limited. Try to roll across the strings in such a way that your transition from A to E is less gradual and more assertive; don't slowly "fade" your bow weight from A to E. Finally, there's less danger of whistling when your bow is slightly closer to the bridge, so you can intentionally angle your bow so that it doesn't form a 90-degree angle with the strings, but rather is farther from the bridge on G string and closer to it on E ( ). Go easy on that one, since it's then harder to set the string in motion when you're closer to the bridge (and you definitely don't want to get close enough for a real ponticello sound). You can "drift" back into a normal placement after the E has been set in motion.