A medical device, such as an extra-cardiovascular implantable cardioverter defibrillator (ICD), senses R-waves from a first cardiac electrical signal by a first sensing channel and stores a time segment of a second cardiac electrical signal acquired by a second sensing channel in response to each sensed R-wave. The medical device determines at least one noise parameter from a group of the stored time segments of the second cardiac electrical signal, detects noise based on the noise parameter, and withholds detection of a tachyarrhythmia episode in response to detecting the noise.
