Connecting a 4k7 resistor between signal and ground might stop that.
Sounds like me before I discovered electronics..
"4k7" is electronics representation for 4.7 k ohm . The "k" identifies the decimal point place and the also that it is 1000x the given value so 1000 x 4.7 = 4700 ohms. "OHM" is the unit of measurement for resistance , named after the scientist who discovered it. You can learn more about it by googling OHM'S LAW. FYI, in case you are REALLY REALLY REALLY NOT an electronics guy, resistance is the opposition to the flow of current , that is the electrons (which are negatively charged) are doing their damndest to get to the + terminal by jumping from one copper atom to the next but when they get to the + terminal the attraction of the nearest atom supercedes other forces and they must jump onto other atoms that have lost their electrons due to the same process. The result is that once the connection is made the electrons are flowing. That "flow" has been given the name "current ", so we say "current is flowing " because nobody gives a damn about some stupid electrons jumping around. What gets interesting is that if the Electromotive Force is great enough (voltage is HIGH enough) and the current is great enough, when you try to switch off the power , like with a relay, the electrons leap in masse from the relay contacts in such large quantities that it creates a plasma arc , spot welding the contacts together. When dealing with very high voltages , copper can vaporize and generate a plasma (called arc flash) 10,000 time brighter than the sun, capable of blinding a person permanently from eye damage and the molten copper vapor is propelled in all directions , burning clothes and melting skin on contact. Well, I think that's enough for the primer... Enjoy electronics....!