Alaska's Gareloi volcano, in the Aleutian Islands, appears to be displaying strong harmonic tremor. AVO states "Seismic station GAEA is 3.3 km (2.0 miles) from the summit of Mount Gareloi", so this does appear to be directly monitoring the volcano. Note the increasing strength of the tremor, similar to the tremor recently observed at El Hierro in the Canary Islands during its current eruptive phase. (Image Below)
Gareloi is a very remote volcano on the SE of the Bering Sea, and thus visual reports from the area are few and far between. It is indeed possible that volcanoes regularly erupt in this area without anyone noticing due to inclement weather, and sparse population. The recent eruption/lava dome extrusion that occurred on Cleveland volcano this past few months was only observed through satellite photos, which are expensive to schedule, so it would not surprise me in the very least if AVO never confirms an eruption at Gareloi (although you can email them, and they do usually respond, which is nice).
Gareloi is one of the Aleutian Islands most active volcanoes, having had several historical eruptions. Below is information from Smithsonian GVP:
"The 8 x 10 km diameter Gareloi Island, the northernmost volcano of the Delarof Group at the western end of the Andreanof Islands, consists of a stratovolcano with two summits and a SE-trending fissure. This prominent fissure was formed during an eruption in 1929 and extends from the southern summit to the sea. Steep sea cliffs that are cut into rocks of an older, eroded center are found on the SW coast. Young lava flows cover the older volcano from the 1573-m-high summit of Gareloi to the coast along three broad axes trending NW, ENE, and south. The 1929 eruption originated from 13 craters along a 4-km-long fissure. Phreatic explosions were followed by the ejection of glassy pumice, lapilli, scoria, and older blocks, as well as by the emission of four short, steep lava flows, one of which reached the SE coast."